One of the conventional glass-ceramics useful as biomaterials is the glass-ceramic containing apatite crystals and wollastonite crystals. This glass-ceramic is prepared by the following procedure: grinding the MgO--CaO--SiO.sub.2 --P.sub.2 O.sub.5 system glass with a MgO content of up to 7 wt % to 200 mesh or less powders; compression molding the resulting glass powders; heat-treating the molding in the sintering temperature range of the glass powders; and subsequently heat-treating the sintered glass powder molding in a temperature range where the apatite crystals [Ca.sub.10 (PO.sub.4).sub.6 O] and the wollastonite crystals [CaO.SiO.sub.2 ] are formed. Further, a glass-ceramic obtained from the MgO--CaO--SiO.sub.2 --P.sub.2 O.sub.5 system glass containing 8 wt % or more MgO is known. This glass-ceramic contains apatite crystals and alkaline earth metal silicate crystals such as diopside [CaO.MgO.2SiO.sub.2 ], forsterite [2MgO.SiO.sub.2 ] or akermanite [2CaO.MgO.2SiO.sub.2 ].
In these glass-ceramics, the apatite crystals contribute to their biocompatibility and the alkaline earth silicate crystals such as wollastonite, diopside, forsterite and akermanite contribute to the mechanical strength of the glass-ceramics. Therefore, in order to provide a glass-ceramic having not only good biocompatibility but also high mechanical strength, the contents of both apatite crystals and alkaline earth metal silicate crystals are desirably increased.
The conventional glass-ceramic useful as a biomaterial has a bending strength of about 1,200 to 1,400 kg/cm.sup.2 in the glass-ceramic with a MgO content of up to 7 wt %, and about 1,500 to 1,800 kg/cm.sup.2 in the glass-ceramic with a MgO content of 8 wt % or more. These values, however, are not completely satisfactory for the purpose of using such glass-ceramic as artificial dental roots or artificial bones.
It is known that tricalcium phosphate crystals are a component which is absorbed into a living body to derive bone formation. A material wherein a sintered product of the tricalcium phosphate is arranged on the surface of a polymethyl methacrylate is used as an artificial dental root, and a porous sintered product of the tricalcium phosphate crystal is used as a substitute for bone.
The tricalcium phosphate crystal has the characteristic that the crystal is absorbed in the living body to derive the bone formation as described above. However, due to this characteristic, where the sintered product of the crystal is actually used as the implant material, the material must be designed, taking into consideration the absorption rate into living body and the bone formation rate.